The fabrication of semiconductor devices involves forming electronic components in and on semiconductor substrates, such as silicon wafers. These electronic components may include one or more conductive layers, one or more insulation layers, and doped regions formed by implanting various dopants into portions of a semiconductor substrate to achieve specific electrical properties. Semiconductor devices include transistors, resistors, capacitors, and the like, with intermediate and overlying metallization patterns at varying levels, separated by dielectric materials, which interconnect the semiconductor devices to form integrated circuits.
Silicides (metal-semiconductor alloys) are used in the semiconductor industry to enhance signal propagation through transistors and other conductive features of semiconductor devices. A silicide has a lower resistance than the underlying doped silicon or poly. As a result, contact resistance is reduced and signal propagation through the semiconductor device is enhanced.
Current nanoscale semiconductor devices employ embedded conductive regions, such as source/drain (S/D) regions for a field effect transistor (FET). For different device regions and various devices (e.g., nFET, pFET), these embedded conductive regions may be grown with different overfills. For example, S/D regions in one device region may be raised above a semiconductor substrate farther than S/D regions in a second device region. In another example, S/D regions in the second device region may not be raised above the substrate at all.
Since known etching methods have poor selectivity to typical semiconductor substrates (e.g., Si, SiGe, SiC), to expose conductive regions of a plurality of semiconductor devices in a substrate, a timed etch, such as a reactive-ion etch (RIE), is used, with the time determined by the lowest of the conductive regions to ensure that good contact is made to all conductive regions. A consequence of this is that the conductive regions with a higher overfill end up with significant recessing that can cause device performance degradation and/or high junction leakage.
The characteristics of the silicide, e.g., thickness, resistance, and the like, may be controlled through various parameters such as the type of metal, annealing time and temperature, etc.